Bearing structure for gear in external gear pump

ABSTRACT

A gear bearing structure for an external gear pump includes a driving gear and the driven gear accommodated rotatably in a pump body of the external gear pump, an inlet chamber formed on one side of a mesh portion of the driving gear and the driven gear, an outlet chamber formed on the other side of the mesh portion, a hollow cylindrical bushing for holding a rotational shaft of the driving gear or the driven gear with a lubricating liquid film formed between itself and the rotational shaft, and a ring plate spring disposed between the pump body and the bushing to urge the bushing so as to slidably contact with a side face of the one of the driving gear and the driven gear.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of International Application No. PCT/JP2021/036031, filed on Sep. 30, 2021, which claims priority to Japanese Patent Application No. 2020-211215, filed on Dec. 21, 2020, the entire contents of which are incorporated by reference herein.

BACKGROUND 1. Technical Field

The present disclosure relates to a bearing structure for a gear in an external gear pump that pumps out fluid by a pair of gears.

2. Description of the Related Art

A Japanese Patent Application Publication No. 2000-145661 (Patent Literature 1) discloses an external gear pump. The external gear pump includes a pair of a driving gear and a driven gear in its pump body. Gear teeth are formed on each outer circumference of the driving gear and the driven gear. The driving gear and the driven gear are held by side plates from both sides in an axial direction while meshing with each other. An inlet chamber is formed on one side of the meshing portion of the driving gear and the driven gear, and a discharge chamber is formed on the other side of the meshing portion.

The driving gear and the driven gear begin to engage on the discharge chamber side and disengage on the suction chamber side. Fluid enters between the disengaged gear teeth, and the fluid delivered along circumferential directions toward the discharge chamber as the gear teeth rotate while being held between the gear teeth and the inner surfaces of the pump body. Each rotating shaft of the driving gear and the driven gear is supported by a fluid bearing. In the fluid bearing, a lubricating liquid film is formed between an inner surface of each bushing that supports a rotating shaft and an outer surface of the rotating shaft by the fluid delivered by the gear pump. In addition, the side surfaces of the gears slidably contact end surfaces of the bushings.

SUMMARY

If the fluid leaks from the sliding contact surface between the bushings and the gears, the efficiency of the gear pump will be reduced. In addition, if accuracy is required for the discharge volume of the pump, the leakage of the fluid from the sliding contact surfaces will reduce the accuracy of the discharge volume. An object of the present disclosure is to provide a bearing structure for a gear in an external gear pump that can suppress leakage of fluid and pump out the fluid with stable accuracy.

A bearing structure for a gear in an external gear pump according to the present disclosure includes: a driving gear and the driven gear that are accommodated rotatably in a pump body of the external gear pump; an inlet chamber that is formed on one side of a mesh portion of the driving gear and the driven gear; an outlet chamber that is formed on another side of the mesh portion; a bushing that is hollow cylindrical, and holds a rotational shaft of one of the driving gear and the driven gear with a lubricating liquid film formed between itself and the rotational shaft; and a ring plate spring that is disposed between the pump body and the bushing, and urges the bushing so as to slidably contact with a side face of the one of the driving gear and the driven gear.

The ring plate spring may be a wave washer having a waving shape along a circumferential direction thereof.

The bearing structure for a gear may further includes a flow passage for introducing fluid from the outlet chamber to a position where the ring plate spring is located.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an external gear pump that includes a bearing structure for a gear according to a first embodiment;

FIG. 2 is a cross-sectional view taken along a line II-II in FIG. 1 ;

FIG. 3 is a cross-sectional view taken along a line III-III in FIG. 1 ;

FIG. 4 is an exploded perspective view showing a bush and a ring plate spring in the first embodiment;

FIG. 5 is a perspective view showing another end of the bush;

FIG. 6 is a perspective view showing a circular protrusion of a mid plate of the external gear pump;

FIG. 7 is a perspective view showing a high-pressure supply passage formed in a pump body of the external gear pump;

FIG. 8 is a cross-sectional view of an external gear pump that includes a bearing structure for a gear according to a second embodiment (figure corresponding to FIG. 1 ); and

FIG. 9 is an exploded perspective view showing a bush and a ring plate spring in the second embodiment (figure corresponding to FIG. 4 ).

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, exemplary embodiments will be explained with reference to the drawings. First, a bearing structure for a gear according to a first embodiment will be explained with reference to FIG. 1 to FIG. 7 .

An external gear pump P that includes the bearing structure for a gear according to the first embodiment is used as a pump for delivering liquid fuel to an engine. Hereinafter, the external gear pump P is also called merely as the gear pump P, and this liquid fuel is also called merely as the fuel. In the gear pump P, the fuel is also utilized as lubricating liquid that lubricates various portion of the gear pump P. Hereinafter, the lubricating liquid is also called as lubricating oil. Thus, the fuel and the lubricating oil are identical to each other in the present embodiment. Depending on contents of explanations, both terms, the fuel and the lubricating oil, are used hereinafter.

As shown in FIG. 1 and FIG. 2 , the gear pump P includes a pair of gears G within its pump body B. In the present embodiment, the pump body B is configured of a main body B1, a side plate B2, a mid plate B3 and an end plate B4. A gear accommodation chamber 1 that accommodates the pair of the gears G in a state where they are meshed with each other is formed within the main body B1. The gear accommodation chamber 1 has an 8-shaped cross-section on a cross-sectional plane perpendicular to rotational axes O of the gears G.

The gears G will be explained later in detail, but plural gear teeth are formed on each outer circumference of the gears G. Tip ends of the gear teeth are in sliding contact with the inner circumferential surfaces of the gear accommodation chamber 1 with a lubricating oil film formed therebetween. An inlet chamber 2I to which the fuel is supplied from outside is formed on one side of a constriction portion of the gear accommodation chamber 1, i.e. the meshed portion of the gears G, and an outlet chamber 2O from which the fuel is discharged is formed on the other side thereof. The gear pump P is a positive displacement pump, and the pressure PH in the outlet chamber 2O is higher than the pressure PL in the inlet chamber 2I (PL<PH) due to flow resistance on a side of the outlet chamber 2O and so on.

The side plate B2 and the mid plate B3 are fixed with the main body B1 by bolts 3 or the like from both sides in a direction of the above-mentioned rotational axes O, respectively. Note that bolts on a side of the side plate B2 are not shown in the drawings. Both ends of each rotational shaft GS of the gears G are rotatably held by the side plate B2 and the mid plate B3, respectively, via after-explained hollow cylindrical bushings F. The bushings F will be explained later in detail, but each of the bushings F constitutes a liquid bearing that utilizes a lubricating liquid film formed between its inner circumferential surface 100 (see FIG. 4 and FIG. 5 ) and the outer circumferential surface of the rotational shaft(s) GS. This liquid bearing is also a plain bearing. The ring-shaped end plate B4 is fixed on the outer side surface of the mid plate B3. The rotational shaft GS of the one of the paired gears G, i.e. the rotational shaft GS1 of the first gear G1, is extended out from the center of the end plate B4.

The first gear G1, which is the one of the paired gears G, is a driving gear that is rotated by external power. Splines are formed on an end of the rotational shaft GS1 of the first gear G1 (see FIG. 7 ), and the first gear G1 is connected with its drive source via the splines. The second gear G2, which is the other of the paired gears G, is a driven gear that is rotated along with the rotations of the first gear G1. The first gear G1 and the second gear G2 rotate in opposite directions to each other as shown by arrows in FIG. 2 . Gear profiles, such as the shape and the numbers of the gear teeth and so on, of the first gear G1 and the second gear G2 are identical to each other. The fuel in the inlet chamber 2I is carried along the inner circumferential surface of the gear accommodation chamber 1 in a state where it is held between the gear teeth of the first gear G1 and the second gear G2 to be delivered to the outlet chamber 2O.

The rotational shaft GS1 of the first gear G1 is a solid circular shaft, and is formed monolithically with the first gear G1 so as to pass through the first gear G1. An oil seal S for preventing leakage of the lubricating oil while allowing the rotations of the rotational shaft GS1 is provided between the rotational shaft GS1 and the side plate B2. An oil seals S for preventing leakage of the lubricating oil while allowing the rotations of the rotational shaft GS1 is also provided between the rotational shaft GS1 and the mid plate B3. On the other hand, the rotational shaft GS2 of the second gear G2 is a hollow circular shaft, and is formed monolithically with the second gear G2 so as to pass through the second gear G2. Both ends of the rotational shaft GS2 are held by the side plate B2 and the mid plate B3, respectively, via the bushings F. The lubricating oil can flow through the inside of the rotational shaft GS2.

A portion of the rotational shaft GS1 of the first gear G1 on a side of the mid plate B3 is held by the first bushing F11, and its portion on a side of the side plate B2 is held by the second bushing F12. Similarly, a portion of the rotational shaft GS2 of the second gear G2 on a side of the mid plate B3 is held by the first bushing F21, and its portion on a side of the side plate B2 is held by the second bushing F22. The first bushing F11 of the first gear G1 and the first bushing F21 of the second gear G2 are configured symmetrically to each other with respect to a symmetrical plane that is located at the center between the first gear G1 and the second gear G2 and is parallel to the rotational axes O of the rotational shafts GS as shown in FIG. 3 . However, with respect to the first bushing F11 of the first gear G1 and the first bushing F21 of the second gear G2, shapes of their low pressure depressed portions 101 and high pressure depressed portions 102 a that will be explained later are slightly different from each other, respectively.

The first bushings F11 and F21 that are configured symmetrically to each other will be explained hereinafter with reference to the first bushing F11 shown in FIG. 4 and FIG. 5 . The first bushing F11 has a hollow cylindrical shape, and a stepped portion is formed on its outer circumferential surface. A ring-shaped second surface P2 is formed on the stepped portion. In other words, a large diameter portion and a small diameter portion are formed in the first bushing F11 with the second surface P2 as a border, and an outer diameter of the large diameter portion is the same as a gear outer diameter of the first gear G1 (see FIG. 2 ). Lubrication grooves 103 are formed on the outer circumferential surface of the large diameter portion to facilitate sliding of the rotational shaft GS in its axial direction.

A portion of the outer circumferential surface of the large diameter portion of the first bushing F11 is formed as a contact flat face 104. The first bushings F11 and F21 are disposed on a side of the mid plater B3 within the gear accommodation chamber 1 in a state where this contact flat face 104 is planarly contacted with the contact flat face 104 of the first bushing F21 of the second gear G2. Therefore, the first bushings F11 and F21 are accommodated non-rotatably in the gear accommodation chamber 1. The plane containing the contact flat faces 104 is the above-mentioned symmetrical plane of the bushings F11 and F21. The inner diameter of the inner circumferential surface 100 of the first bushing F11 is approximately equal to the outer diameter of the rotational shaft GS1 of the first gear G1, and the lubricating liquid film is formed between the inner circumferential surface 100 and the rotational shaft GS1. That is, the inner circumferential surface 100 is in sliding contact with the outer circumferential surface of the rotational shaft GS1 through the lubricating liquid film.

The second surface P2 is a flat surface perpendicular to the rotational axis O1 of the rotational shaft GS1, and is opposed to a first surface P1 (see FIG. 6 ) of a circular protrusion 6 (see FIG. 1 ) of the mid plate B3. And, a ring plate spring 4 is interposed between the second surface P2 and the first surface P1 (see FIG. 4 ). The ring plate spring 4 in the present embodiment is a wave washer formed by metal having springiness. The ring plate spring 4 is disposed between the second surface P2 and the first surface P1, i.e. between the pump body B and the first bushing F11, in a compressed state to urge the first bushing F11 to the side face of the first gear G1. The rotational shaft GS1 is inserted into the center hole of the ring plate spring 4.

The ring plate spring 4 in the present embodiment is a wave washer in the form of a circumferential four-cycle wave that contacts each of the first surface P1 and the second surface P2 at four locations. In order to urge the first bushing F11 precisely in a direction of the rotational axis O1 of the rotational shaft GS1 toward the side face of the first gear G1, it is desirable to contact each of the first surface P1 and the second surface P2 at three or more locations. In addition, it is also desirable that the contact locations with each of the first surface P1 and the second surface P2 are arranged evenly along the circumferential direction. In the present embodiment, the width of the ring plate spring 4 is set to conform to the position where the width of the second surface P2 is narrowest. Since the width of the second surface P2 is narrowest at the center of the above-mentioned contact flat face 104, the width of the ring plate spring 4 is made approximately equal to, or specifically made slightly narrower than, this width.

The first bushing F11 has a third surface P3 that faces to the first gear G1. The third surface P3 is also a flat surface perpendicular to the rotational axis O1 of the rotational shaft GS1, and is in sliding contact with the side face of the first gear G1 through the lubricating oil film. The low pressure depressed portion 101 is formed from the third surface P3 to the outer circumferential surface and a portion of the contact flat face 104 on a side of the inlet chamber 2I. A concave inner surface of the low pressure depressed portion 101 is part the inlet chamber 2I. The high pressure depressed portion 102 a is formed from the third surface P3 to the outer circumferential surface and a portion of the contact flat face 104 on a side of the outlet chamber 2O. A concave inner surface of the high pressure depressed portion 102 a is an inner surface of the outlet chamber 2O. A tapered portion 102 b is extended from the high pressure depressed portion 102 a along the circumferential direction. The tapered portion 102 b forms a tapered surface between the third surface P3 and the outer circumferential surface. The first bushing F11 has a fourth surface P4 that faces to the mid plate B3. The fourth surface P4 is also a flat surface perpendicular to the rotational axis O1 of the rotational shaft GS1.

Here, pressure ranges formed along the circumferential direction of the pair of the gears G will be explained with reference to FIG. 3 . As explained above, the pressure PH in the outlet chamber 2O is higher than the pressure PL in the inlet chamber 2I (PL<PH). Therefore, along the inner circumference of the gear accommodation chamber 1 associating with the outer circumference of the first gear G1 and the second gear G2, a low pressure range L is formed in association with the inlet chamber 2I. This low pressure range L associates with the above-explained low pressure depressed portions 101. On the other hand, along the inner circumference of the gear accommodation chamber 1 associating with the outer circumference of the first gear G1 and the second gear G2, a high pressure range H is formed in association with the outlet chamber 2O. This high pressure range H associates with the above-explained high pressure depressed portions 102 a. Here in the present embodiment, the high pressure depressed portions 102 a is extended along the circumferential direction by the tapered portions 102 b as explained above. Therefore, the high pressure range H in the present embodiment is extended to the tapered portions 102 b.

As explained above, the fuel is delivered in the circumferential direction in a state where it is held between the gear teeth of the gears G. During this process, the pressure of the fuel held between the gear teeth takes a lower pressure within the low pressure range L, and takes a high pressure within the high pressure range H. Pressure transition ranges T in which the pressure of the fuel gradually transfers from a low pressure to a high pressure via the lubricating oil film at the sliding contact portions are formed between the low pressure range L and the high pressure range H. The pressure transition ranges T can be also called as pressure rising ranges. In this manner, the low pressure range L, the pressure transition ranges T and the high pressure range H are segmented in association with the outer circumference of the gears G.

A pass through groove 107 is formed on the inner circumferential surface 100 of the first bushing F11. The pass through groove 107 is located within the above-mentioned high pressure range H (see FIG. 3 ). The pass through groove 107 is formed parallel to the rotational axis O1 of the rotational shaft GS1 along an entire length of the inner circumferential surface 100 from its one end to its other end. An inner surface of the pass through grove 107 is formed as a concave surface. One end of the pass through groove 107 on a side of the fourth surface P4 communicates with the low pressure lubricating oil in the inlet chamber 2I through the inside of the mid plate B3. The lubricating oil in the pass through groove 107 forms the lubricating liquid film between the inner circumferential surface 100 of the first bushing F11 and the outer circumferential surface of the rotational shaft GS1. The lubricating oil that forms the lubricating liquid film is discharged by the pass through groove 107 from its low pressure end on a side of the fourth surface P4, and the sliding surface is cooled by the circulation of the lubricating oil.

As explained above, the second surface P2 of the first bushing F11 or F21 faces to the first surface P1 of the mid plate B3. The first surface P1 is also a flat surface perpendicular to the rotational axes O of the rotational shafts GS. As shown in FIG. 6 , the first surface P1 is formed as an end face of a circular protrusion 6 of the mid plate B3. The circular protrusion 6 is protruded from a surface, which faces to the main body B1, of the mid plate B3. A first accommodation hole H1 that accommodates an end of the first bushing F11 and a second accommodation hole H2 that accommodates an end of the first bushing F21 are formed on the first surface P1 of the circular protrusion 6. The first accommodation hole H1 is a through hole provided with a step on its inner circumferential surface, and the rotational shaft GS1 of the first gear G1 passes through this through hole. The second accommodation hole H2 is a bottomed hole.

The first accommodation hole H1 accommodates the small diameter portion of the first bushing F11. Therefore, the second surface P2 that is the border between the small diameter portion and the large diameter portion of the first bushing F11 faces to the first surface P1. Similarly, the second accommodation hole H2 accommodates the small diameter portion of the first bushing F21. Therefore, the second surface P2 that is the border between the small diameter portion and the large diameter portion of the second bushing F21 also faces to the first surface Pl. The above-explained ring plate spring 4 in the compressed state contacts the first surface P1 and the second surface P2, and thereby urges the first bushings F11 and F21 in the direction away from the first surface P1.

Seal grooves 7 each accommodates an O ring for preventing leakage of the lubricating oil are formed on the outer circumferential surface of the circular protrusion 6 and on the inner circumferential surfaces of the first accommodation hole H1 and the second accommodation hole H2, respectively. FIG. 6 shows also a high-pressure supply passage 5 for supplying the high pressure lubricating oil to a position between the second surface P2 and the first surface P1. Although the high-pressure supply passage 5 will be explained later in detail, an open end 5 c that is an outlet end of the high-pressure supply passage 5 in the present embodiment is branched to have a T-shape, and its one end faces to the second surface P2 of the first bushing F11 and its other end faces to the second surface P2 of the first bushing F21. Thus, the open end 5 c faces to the second surfaces P2 of both of the first bushing F11 and the first bushing F21. The high pressure lubricating oil supplied between the first surface P1 and the second surfaces P2 urges the first bushings F11 and F21 together with the ring plate spring 4.

Hereinbefore, the first bushing F11 or F21 disposed on a side of the mid plate B3 has been explained. In the present embodiment, the second bushing F12 or F22 disposed on a side of the side plate B2 is partially different from the first bushing F11 or F21. No ring plate spring 4 is disposed at a location of the second surface P2 of the second bushing F12 or F22. In addition, the second bushing F12 has an almost symmetrical shape to that of the first bushing F11 with respect to the first gear G1, and the second bushing F22 has an almost symmetrical shape to that of the first bushing F21 with respect to the second gear G2. The lubricating oil in the pass through groove 107 forms the lubricating liquid film between the inner circumferential surface 100 of the first bushing F21 and the outer circumferential surface of the rotational shaft GS1. The lubricating oil that forms the lubricating liquid film is discharged by the pass through groove 107 from its low pressure end on a side of the fourth surface P4, and the lubricated sliding surface is cooled by the circulation of the lubricating oil. The fourth surface P4 of the second bushing F22 that faces to the side plate B2 and the fourth surface P4 of the first bushing F21 that faces to the mid plate B3 are communicated with each other through the inside of the rotational shaft GS2 of the second gear G2.

The second bushings F12 and F22 are accommodated in the gear accommodation chamber 1 on a side of the side plate B2. Here, as explained above, the first bushings F11 and F21 are urged in the direction away from the first surface P1 (leftward in FIG. 1 ). In other words, the first bushings F11 and F21 are urged toward the pair of the gears G. Since the second surfaces P2 of the second bushings F12 and F22 contact with stepped portions of the main body B1, their positions along the direction of the rotational axes O the rotational shafts GS are fixed. The pair of the gears G are pushed by the urged first bushings F11 and F21, and thereby their side faces are in sliding contact with the third surfaces P3 of the second bushings F12 and F22 with the lubricating oil film formed therebetween. Note that, as explained above, the pair of the gears G are in sliding contact also with the third surfaces P3 of the urged first bushings F11 and F21 at their opposite side faces. In this manner, the sliding contact state of the gears G, the first bushings F11 and F21, and the second bushings F12 and F22 is made stable.

The high-pressure supply passage 5 will be explained with reference to FIG. 7 . Note that the ring plate spring 4 is now shown in FIG. 7 in order to make the figure easier to see. A supply port 8 for supplying the high pressure lubricating oil to the high-pressure supply passage 5 is provided on an outer surface of the mid plate B3. The supply port 8 is connected with a discharge port 9 for discharging the high pressure fuel from the outlet chamber 2O by a pipe(s) (not shown in the figure). A main passage of 5 a the high-pressure supply passage 5 is formed straight from the supply port 8 toward a position on a slightly outer side of the circular protrusion 6. The main passage 5 a is formed perpendicular to the rotational axes O of the rotational shafts GS. A supplementary passage 5 b of the high-pressure supply passage 5 is connected to the end of the main passage 5 a (also see FIG. 6 ). The supplementary passage 5 b is formed parallel to the rotational axes O of the rotational shafts GS, i.e. perpendicular to the first surface P1. Then, the above-explained open end 5 c branched to have the T-shape is formed at the end of the supplementary passage 5 b.

Note that the high-pressure supply passage 5 may be formed within the pump body B so as to connect the open end 5 c with the outlet chamber 2O. The high-pressure supply passage 5 is part of a passage for introducing fluid from the outlet chamber 2O to the position where the ring plate spring 4 is disposed, i.e. the position between the first surface P1 and the second surface P2. Since the minute gap between the first surface P1 and the second surface P2 doesn't faces the sliding contact surface in the present embodiment, the lubricating oil can be kept at high pressure along its entire circumference. Furthermore, the ring plate spring 4 is also interposed between the first surface P1 and the second surface P2, and thereby the minute gap between the first surface P1 and the second surface P2 functions as a storage of the high pressure lubricating oil. As the result, the high pressure lubricating oil can be supplied from the open end 5 c to the position between the first surface P1 and the second surface P2.

In the gear pump P having the above-explained configuration, the lubricating oil can transfer through the lubricating liquid films formed between the circumferential surfaces of the gears G and the pump body B, between the side faces of the gears G and the third surfaces P3, and between the outer circumferential surfaces of the rotational shafts GS and the inner circumferential surfaces 100 of the bushings F. However, in the present embodiment, the high pressure lubricating oil is supplied to the position between the second surfaces P2 of the first bushings F11 and F21 and the first surface P1 of the mid plate B3, and the ring plate springs 4 are also interposed between the second surfaces P2 and the first surface P1. Therefore, the leakage of the lubricating oil between the side faces of the gears G and the third surface P3 can be restricted by urging the first bushings F11 and F21 toward the side faces of the gears G by use of the pressure of the lubricating oil and the ring plate springs 4. As the result, decrease in efficiency of the gear pump can be restricted. In addition, since the leakage of the lubricating oil between the side faces of the gears G and the third surface P3 can be restricted, degradation in accuracy of the discharge volume of the fuel can be also restricted.

Furthermore, the pressure PH of the lubricating oil in the outlet chamber 2O is utilized for the lubricating oil pressure for urging the gears G in the present embodiment as explained above. The ring plates 4 urge the first bushings F11 and F21 toward the side faces of the gears Gin the present embodiment even when the pressure PH in the outlet chamber 2O is low, and thereby the leakage of the lubricating oil between the side faces of the gears G and the third surfaces P3 can be restricted. On the other hand, when the pressure PH in the outlet chamber 2O increases, it may seem that the leakage of the lubricating oil between the side faces of the gears G and the third surfaces P3 within the above-mentioned high pressure range H (see FIG. 3 ) will likely increase. However, the pressure PH is also applied to the position between the second surfaces P2 and the first surface P1 in the present embodiment, and thereby the urging force for the first bushings F11 and F21 by the lubricating oil pressure and the ring plate springs 4 also increases. Therefore, the leakage of the lubricating oil between the side faces of the gears G and the third surfaces P3 can be kept restricted.

Here, the above-explained urging structure including the ring plate spring(s) 4 will be compared with a following urging structure. In the urging structure as the comparative example, plural accommodation holes for accommodating compressed coil springs are formed on the second surfaces P2 along its circumferential direction to urge the first bushing s F11 and F21 toward the side faces of the gears G by the plural coil springs. However, the number of parts increases in this comparative example due to the coil springs. In addition, production processes, such as a work process for forking the accommodation holes and a process of accommodating the coil spring into the accommodation holes, also increase. Furthermore, the production processes become complex, because its assembling should be done while the coil springs are being accommodated within the accommodation holes. Therefore, the production of the gear pump P becomes complex. On the other hand, according to the bearing structure for a gear in this disclosure including the ring plate spring 4, such a problem can be avoided, because the ring plate spring 4 is self-aligned when each small-diameter portion of the first bushings F11 and F21 is inserted into them.

In addition, it is inevitable in the comparative example to make the radial width of the second surface P2 wide, i.e. to make the area of the second surface P2 large, in order to form the accommodation holes, in other words, to make the area of the first surface large. Since the pressure PH in the outlet chamber 2O is utilized for urging the first bushings F11 and F21, this means the area that receives the pressure PH becomes large. Therefore, it is concerned that the urging force for the first bushings F11 and F21 becomes excessively high when the number of rotations of the gears G increases and then the pressure PH becomes high. The excessive urging force for the first bushings F11 and F21 increases rotational frictions of the gears G, and thereby causes reductions of the pump efficiency and abrasions of the gears G and the bushings F. Therefore, this configuration of the comparative example may restrict design flexibility of the gear pump P. On the other hand, since the ring plate spring 4 is used in the present embodiment, design flexibility of the radial width of the second plane P2 becomes high and thereby design flexibility of gear pump P can be improved. More specifically, it can be easily done to set a ratio of an area of the second surface P2 on the high-pressure side and an area of the fourth surface P4 on the low-pressure side, and thereby design flexibility of the urging force by the lubricating oil pressure can be made high.

Next, a bearing structure for a gear according to a second embodiment will be explained with reference to FIG. 8 and FIG. 9 . A position where the ring plate spring 4 is provided in the present embodiment is different from that in the first embodiment. Hereinafter, only configurations different from those of the first embodiment will be explained. Configurations equivalent and similar to those of the first embodiment will be labelled with identical numbers, and their detailed explanations will be omitted.

In the present embodiment, the ring plate springs 4 are provided between the fourth surface P4 of the first bushing F11 and the bottom surface of the first accommodation hole H1, and between the fourth surface P4 of the first bushing F21 and the bottom surface of the second accommodation hole H2 (see also FIG. 6 ). The first accommodation hole H1 and the second accommodation hole H2 are formed on the circular protrusion 6 of the mid plate B3, as described above. FIG. 9 shows only the first bushing F11 among the first bushing F11 and the second bushing F21, but a portion on a side of the second bushing F21 is also symmetrically configured similarly to the first embodiment. Following explanations will be made with reference to the first bushing F11 shown in FIG. 9 .

The ring plate spring 4 of the present embodiment is also a wave washer formed by metal having springiness. The ring plate spring 4 is disposed between the fourth surface P4 and the bottom surface of the first accommodation hole H1, i.e.

between the pump body B and the first bushing F11, in a compressed state to urge the first bushing F11 toward the side face of the first gear G1. The rotational shaft GS1 is inserted into the center hole of the ring plate spring 4. The ring plate spring 4 in the present embodiment is also a wave washer in the form of a circumferential four-cycle wave. The width of the ring plate spring 4 is almost equal to the width of the fourth surface P4.

Although the pressure PL in the inlet chamber 2I is introduced to the position where the ring spring 4 is located i.e. between the fourth surface P4 and the bottom surface of the first accommodation hole H1 as explained above, the pressure PH in the outlet chamber 2O is introduced to the position between the first surface P1 and the second surface P2 also in the present embodiment. Therefore, the first bushing F11 urged toward the side face of the first gear G1 by the ring plate spring 4 and the pressure PH. Note that, while assembling the gear pump P, the ring plate spring 4 is self-aligned when being attached to the rotating shaft GS1.

The leakage of the lubricating oil between the side faces of the gears G and the third surface P3 can be restricted by urging the first bushings F11 and F21 toward the side faces of the gears G by use of the pressure of the lubricating oil and the ring plate springs 4 according to the present embodiment similarly to the above-explained first embodiment. As the result, decrease in efficiency of the gear pump can be restricted. In addition, since the leakage of the lubricating oil between the side faces of the gears G and the third surface P3 can be restricted, degradation in accuracy of the discharge volume of the fuel can be also restricted. Furthermore, in the present embodiment, the design flexibility of the area of the second surface P2, i.e. the design flexibility of the urging force for the first bushings F11 and F21 by the pressure of the lubricating oil, is higher than that in the first embodiment.

The first and second embodiments have been explained, but the bearing structure for the gear according to the present embodiment is provided with the hollow cylindrical bushing(s) F for supporting the drive shaft(s) GS. The bushing F forms the lubricating liquid film between it and the rotational shaft GS of at least one of the driving gear G1 and the driven gear G2. In addition, the bearing structure for the gear according to the present embodiment is located between the pump body B and the bushing F, and provided with the ring plate spring 4 that urges the bushing F toward the side face of at least one of the driving gear G1 and the driven gear G2. Therefore, the leakage of the fluid through the position between the bushing F and the side face of the driving gear G1 or the driven gear G2 can be restricted by the ring plate spring 4. As the result, the fluid can be discharged with stable discharge accuracy by restricting the leakage of the fluid.

Here, when the ring plate spring 4 is a wave washer having a shape waving in its circumferential direction, it is possible to urge the bushing F stably toward the side face of the driving gear G1 or the driven gear G2. Since the wave washer has the shape waving in its circumferential direction, it can urges the bushing F evenly along its entire circumference, and thereby can urge the bushing F accurately in the direction of the rotational shaft GS of the gear G. Therefore, the third surface P3 of the bushing F can be slidably contacted with the side face of the gear G, and thereby the leakage of the fluid can be restricted stably. As the result, the fluid can be discharged with more stable discharge accuracy.

In addition, in the present disclosure (the first embodiment), the high-pressure supply passage 5 that is the flow passage for introducing the fluid from the outlet chamber 2O to the position where the ring plate spring 4 is located, i.e. the position between the first surface P1 and the second surface P2. Therefore, it is possible to urge the bushing F stably toward the side face of the driving gear G1 or the driven gear G2 by the high pressure PH in the outlet chamber 2O and the ring plate spring 4. Since the position where the ring plate spring 4 is located, i.e. the position between the first surface P1 and the second surface P2, functions as the storage of the supplied fluid, the pressure can be applied to the bushing F stably. And, when the urging of the bushing F can be ensured by the ring plate spring 4 even when the number of rotations of the gear G is low. On the other hand, when the pressure PH increased due to the increase of the number of rotations, the bushing F is urged by the said pressure PH, and thereby the leakage of the fluid can be restricted stably even when the number of rotations increases. As the result, the fluid can be discharged with more stable discharge accuracy.

Although several embodiments have been described herein, it is to be understood that other variations and modifications of the embodiments are possible in light of the above-disclosed contents. All the configurational elements of the above embodiments and all the features recited in the claims can be arbitrarily combined with each other as long as they do not contradict each other.

For example, the ring plate spring 4 is a wave washer having a perfect seamless ring shape in the above embodiments. However, the ring plate spring 4 may be a single-winding type wave spring that is cut in its radial direction. In this case of the single-winding type wave spring, it may be a C-shape in which its cut ends are distanced, a ring shape in which its cut ends overlap one another. In addition, the ring plate spring 4 may be a disc spring. Even in a case of a disc spring, it may be a disc spring a lot of cut slots are formed from one or both of its inner circumferential edge and its outer circumferential edge. Furthermore, it is preferable that the ring plate spring 4 is provided for both of the driving gear and the driven gear, but it may be provided only for one of them. The above-explained advantages can be brought for the gear for which the ring plate spring 4 is provided. 

What is claimed is:
 1. A bearing structure of a gear for an external gear pump, the structure comprising: a driving gear and the driven gear that are accommodated rotatably in a pump body of the external gear pump; an inlet chamber that is formed on one side of a mesh portion of the driving gear and the driven gear; an outlet chamber that is formed on another side of the mesh portion; a bushing that is hollow cylindrical, and holds a rotational shaft of one of the driving gear and the driven gear with a lubricating liquid film formed between itself and the rotational shaft; and a ring plate spring that is disposed between the pump body and the bushing, and urges the bushing so as to slidably contact with a side face of the one of the driving gear and the driven gear.
 2. The bearing structure of a gear for an external gear pump according to claim 1, wherein the ring plate spring is a wave washer having a waving shape along a circumferential direction thereof.
 3. The bearing structure of a gear for an external gear pump according to claim 1, further comprising a flow passage for introducing fluid from the outlet chamber to a position where the ring plate spring is located.
 4. The bearing structure of a gear for an external gear pump according to claim 2, further comprising a flow passage for introducing fluid from the outlet chamber to a position where the ring plate spring is located. 